Converting Fortran to MATLAB

Greetings, all

I have found a powerful yet compact Fortran code which I am trying to reprogram into MATLAB. Unfortunately, I have now hit a point where I need some help with the logic. The algorithms are easy enough to convert, so I'm not going to show them (unless you really want me to).

My problem is converting the Fortran "GOTO" logic into MATLAB. I have decided to study the sequence in which things happen, and from this created a map of triggers (e.g. if...goto 23 (else) goto 13) and I need to design my loops and functions around these. Some are simple enough (those in the green frames), but one of them (red frame) really has me baffled...

The nested loop between 15 and 19 is just three "for" loops, which are easily coded but less easily illustrated here. They are terminated by 16, 17 and 18 repectively.

From 28 on the calculations are done and some sequential post-processing takes place.

Thanks in advance

Answer 1

[Walter Roberson]

Use "continue" to resume back at point #13. Continue ends the current iteration of the enclosing loop and starts the next iteration.

Matters would be slightly more complicated if you needed to break out of the nested loops and go back to #13, but you do not need to do that so don't worry about it ;-)

[Gerrit Grundling]

Thanks.

This is new to me, but I'll try that.

Answer 2

[Ben Barrowes]

Have you tried the free spag (linux version) from Polyhedron software to clean up (refactor) some of these goto's for you? http://www.polyhedron.com/spag0html

If this doesn't refactor all of your goto's, at least it will get rid of many of them, often 50-75% of them. Spag also declares variables and prettifies the code to some extent so that the conversion to matlab becomes simpler.

If there are goto's left over, you can check out my goto remover (not ready for public consumption, so as yet unpublished) which removes all the remaining goto's using while/break/continue's: http://engineering.dartmouth.edu/~d30574x/consulting/consulting_gotorefactor.html

I would be happy to run your code through this and send it back to you.

Finally, you might try f2matlab at the file exchange to automatically convert the goto-less f90 style code to m-code: http://www.mathworks.com/matlabcentral/fileexchange/5260-f2matlab

f2matlab usually gets you 90-100% towards a working matlab code. You will have to test and debug the resulting code, though.

Good luck!

[Gerrit Grundling]

Thanks, I've finally run enough of it through SPAG to navigate myself through.

I've attached the SPAG result as a text file, starting at line 102.

Answer 3

[Sean de Wolski]

Gerrit,

You might be able to avoid reinventing the wheel by using the MEX api. This will let you compile your fortran code yuo have in a format that MATLAB can use.

http://www.mathworks.com/help/releases/R2013b/matlab/build-fortran-mex-files.html

Then you can just call this rather than rewriting it.

[Gerrit Grundling]

I have to rewrite it eventually, because I need more control over the inputs.

Thanks, though.

Answer 4

[Gerrit Grundling]

Greetings, Ben

I tried SPAG, but it seems that, even after getting rid of the comments and the excess, operations 13 to 28 are too many lines to handle. I'll have to buy the package, but not at that price.

Thanks, though.

[Ben Barrowes]

The evaluation version of spag is free and can handle any number of lines. It will get rid of goto's, but will not change over to f90 format. You might try that version:

http://www.polyhedron.com/pflinux0html

They have windows, linux, and Mac evaluation versions.

Answer 5

[Gerrit Grundling]

Greetings, Walter

Colour me crazy, but doesn't "continue", erm, do nothing...? (In Matlab as it is in Fortran).

[James Tursa]

CONTINUE does not have the same meaning in MATLAB and Fortran:

Do nothing:
MATLAB:   ;
Fortran:  continue

Skip the rest of the current iteration and go to next iteration:
MATLAB:   continue
Fortran:  cycle

[Gerrit Grundling]

Thanks for that explanation, your answer has led me to this curious graphic illustration:

I think I'll try this then.

Answer 6

[Gerrit Grundling]

I have had a moment of inspiration, and decided to rearrange the sequence: instead of going back halfway, it skips steps towards the end. Then I could just use a while loop.

Some other posts on this forum have led me to believe that "continue" is a dangerous tool.

Regards

[Walter Roberson]

"continue" isn't any more dangerous than "break" in MATLAB. The only thing you need to watch out for is if you are in nested loops and want the "continue" to go right out of the inner loop and to the next iteration of the outer loop.